1. Field of the Invention
The present invention relates to an image sensing apparatus and a control method therefor, and more particularly, to an image sensing apparatus and a control method therefor that controls exposure according to a subject satisfying predetermined conditions.
2. Description of the Related Art
Conventionally, there is an image sensing apparatus equipped with an automatic exposure function that determines the exposure automatically with the entire frame being taken into account. In an image sensing apparatus of this type, depending on the scene the determined exposure might cause improper luminance of the main object. In order to obtain the proper luminance for the main object, there are apparatuses in which the user specifies the area in which the main object is present and the apparatus adjusts the exposure based on the specified area. However, such a method burdens the user.
Meanwhile, there is an apparatus having a function that repeatedly detects an object that satisfies predetermined conditions from image data. It is proposed that a camera that acquires the image data using a solid-state image sensing element composed of photoelectric converter elements automatically detects a face that is the main object by a technique such as shape analysis from the obtained image data and controls exposure so that the detected face is properly exposed (see, for example, JP-2003-107555-A). With such a camera, image sensing such that the luminance of the main object is proper no matter what the scene can be carried out.
It should be noted that, as the detection operation in a case in which the face is the main object, a method that detects a person's full face or three-quarter face based on the position of facial features such as the eyes, nose and mouth is proposed in JP-2002-251380-A.
However, with the main object detection method of JP-2002-251380-A, as shown in FIGS. 15A and 15B, both eyes cannot be recognized from the images obtained when the main object blinks his or her eyes (FIG. 15A) or suddenly turns and looks away so that the face is in profile (FIG. 15B). In these instances, the main object cannot be detected, and as a result, it becomes temporarily impossible to detect the main object despite the fact that the main object is in the same place within the frame.
If, for example, the subject is a child who finds it difficult to sit still, when carrying out detection of the main object with the method of JP-2002-251380-A there is a strong possibility that the main object temporarily fails to be detected.
When conducting exposure control so as to detect the main object and get its luminance proper, what is considered proper when the main object is detected differs from what is considered proper when the main object fails to be detected. Consequently, despite sensing the same object, images of different luminances are sensed within a short interval.